The recent progress of the information-oriented society is really remarkable. As a communication method for information communication equipment or information communication service, wireless communication is often used for other than cable communication. With this situation, the demand for the limited resource of radio frequencies is increasing. Therefore, lack of a frequency which can be assigned to the communication is becoming a big problem in some countries. Generally, the frequencies are managed by the country under the license. Only the authorized licensees can use the frequencies in limited places and times, with severe managements. The demand for the frequencies will continue increasing in future. Therefore, corresponding to the demand for the frequencies, the new method of the use of the frequency, not to be seized with past method of the use of the frequency, is needed.
Recently, in order to resolve the problem of lack of frequency, a new method of the utilization of the frequency is being studied. The method may use a frequency band, which has been already assigned to the licensee, but the frequency band is not used in certain spatial and temporal conditions. Such a frequency band may be called a white space. For example, regarding the cognitive wireless communication system, the research and development, or the standardization for this system is currently being enforced. In the cognitive wireless communication system, under the condition that avoiding the influence on the use of the specific frequency for the existing system which is operated by licensed user, the user who has not been licensed to use the frequency can use the frequency flexibly, as a white space. Hereinafter, the user who has an authorized license to use the specific frequency is referred to as a primary user, and the user who has not been licensed to use the specific frequency corresponding to the white space is referred to as a secondary user. For example, those are referred to Non-Patent Literature 1.
As an example, in Wireless Regional Area Network (WRAN) system, using white spaces, being standardizing in IEEE802.22, by accessing a white space database or a coexistence manager on the IP network (hereinafter, database etc.), each radio station can get a list of frequencies available for transmission and allowable maximum transmission electricities, based on its location information. The list of frequencies available for transmission includes the frequency information that can perform wireless communication without giving a primary user interference. The list of frequencies available for transmission is managed collectively while updating the list at any time, by Spectrum Manager (SM) in Base Station (BS), which is connected to Customer Premises Equipment (CPE). In this way, BS can decide an operative frequency based on the list of frequencies available for transmission.
In another case, each radio station (BS or CPE, the same applies hereinafter) may include a spectrum sensing functionality. When each radio station detects the condition that the frequency which is decided by the spectrum sensing functionality, has already been used by a primary user, each radio station notifies Spectrum Manager (SM) of this information. Then, SM can exclude this frequency from the list of frequencies available for transmission. By performing a dynamic spectrum access based on the information changing moment by moment in this way, the wireless communication system using a white space can realize the communication for a secondary user while avoiding influence on use of the frequency for a primary user.
As for the wireless communication system using a white space, various kinds of techniques have been suggested so far. For example, patent literature 1 discloses a wireless communication method using a first base station and a second base station. The first base station can provide first backhaul information to the second base station, by using a shared channel. The shared channel can be supported by a white space channel, Authorized Shared Multi-user (ASM) channel, or Industry Science Medical (ISM) channel. Furthermore, the first base station can provide second backhaul information to the second base station, by using a legacy backhaul channel.
For example, patent literature 2 disclose a wireless communication method, the wireless communication method is comprised of receiving a first signal under using a first channel, deciding a second channel based on the first signal, receiving a second signal under using the second channel, and communicating with a wireless device under using the second channel based on the communication quality of the second signal.